JOAO VICTOR DE SOUSA ARAUJO

JOAO VICTOR DE SOUSA ARAUJO

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Assessment of pitting corrosion in anodized 2xxx aluminum alloys
2023 - ARAUJO, JOAO V. de S.; CHEN, JINGHUI; ZHOU, XIAORONG; COSTA, ISOLDA
This work focus on the characterization of pitting corrosion initiated in 2xxx Al alloys anodized in Tartaric Sulphuric Acid (TSA), specifically the 2024-T3 alloy substrates, and the 2198, in the T8 and T851 tempers. The results were compared to that of anodized pure Al (99.99 wt.%). The pitting corrosion resistance of the anodized samples was tested by potentiodynamic polarization in 0.1 mol L-1 NaCl solution. The tested surfaces were then characterized by optical microscopy, optical profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and image analysis by ImageJ. The polarized samples presented pits of different sizes. Some pits presented diameters of several hundred microns, with the anodic films remaining as pit covers. The pits in all anodized samples showed similar characteristics, such as, a continuous pit cover with a central hole or a pit cover detached from the substrate in some small areas. The central hole serves as a diffusion channel for dissolved species within the pits. Detachment of the pit cover occurs due to accumulation of corrosion products within the pits leading to swelling of the anodic film and its detachment from the substrate. The results showed that pit size and depth analysis measured by optical profilometry can be misleading. Depth assessment should be carried out after removal of the anodic layer followed by crosssection of the anodized sample. The pits developed under highly occluded conditions. It was also observed that in the anodized alloys, as opposed to pure Al, pits are related to the defects in the anodic films due to dissolution of micrometric intermetallic particles during the anodizing process. Pitting attack propagation occurred according to the microstructure characteristics of the tested material.
A homemade electrochemical hanging droplet cell to evaluate the corrosion resistance of friction stir weld zones of the AA2198-T8 Al-Cu-Li alloy
2021 - MACHADO, CARULINE de S.C.; HERNANDEZ, JOSE W.C.; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; DONATUS, UYIME; COSTA, ISOLDA
In this study, the corrosion resistance of the different zones of the AA2198-T8 alloy welded using friction stir welding (FSW) was investigated by immersion and electrochemical tests during exposure to 0.005 mol L-1 NaCl solution. After immersion tests, the welding zones were classified in two groups, according to their severe localized corrosion (SLC) morphology. Zones exposed to higher temperatures during welding presented intergranular attack, whereas those exposed to lower temperatures presented intragranular attack. Electrochemical measurements performed employing a homemade hanging droplet cell revealed potential galvanic coupling between the two groups. The base metal (BM) presented the most anodic potentials. The open circuit potential (OCP) increased from BM towards the stir zone (SZ). The results obtained by the hanging droplet cell were reproducible and coherent with the classification of the zones in the two proposed groups. The homemade electrochemical hanging droplet cell proved a very reliable tool to investigate the electrochemical behavior of the FSWed zones in Al-Cu-Li alloys.
A cerium-based nanocoating for corrosion protection of clad on AA 2024-T3 alloy
2021 - KLUMPP, RAFAEL E.; MACHADO, CARULINE de S.C.; ARAUJO, JOAO V. de S.; ANTUNES, RENATO A.; MAGNANI, MARINA; COSTA, ISOLDA
Aluminum alloys are susceptible to localized corrosion resulting in a major risk for aircrafts due to the extensively use of this material in their structures. Therefore, the surface protection of these alloys against corrosion is fundamental. In this work, an eco-friendly surface pretreatment cerium based for corrosion protection alternatively to chromate based ones was developed and applied on the clad of the 2024-T3 aluminum alloy. The corrosion resistance of the modified surface was evaluated by electrochemical impedance spectroscopy, polarization and Scanning Vibrating Electrode Techniques The results obtained were compared to a chromium based conventional treatment and revealed that the coating layer resulting from the tested treatment resulted in a film composed by spherical nodular nanostructures of cerium that improved the corrosion resistance of the alloy studied and it was comparable to the effect of treatment with hexavalent chromium showing it is an promising alternative to replacing treatments based on environmental harmful treatments.
Microstructural characterization and corrosion behavior of a commercial friction stir welded AA2024-T3
2018 - QUEIROZ, FERNANDA M.; ARAUJO, JOAO V.S.; TERADA, MAYSA; LAMAKA, SVIATLANA; COSTA, ISOLDA; MELO, HERCILIO G. de
Friction Stir Welding (FSW) arises as a great development by removing rivets, fasteners and lap joints areas, consequently, decreasing the aircraft weight. However, during the welding process, the plastic deformation and heat generation at the joint and surrounding areas lead to three distinct microstructural zones, namely, nugget or stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ), besides the base metal (BM). In these zones the microstructure of the material can be profoundly modified and localized corrosion phenomena can be more easily developed, which can be enhanced by local galvanic coupling due to changes in the microstructure as grain refinement and recrystallization, changes in the grain boundaries, dissolution and precipitation of hardening precipitates and dispersóides. In the present work, a commercial friction stir welded AA2024-T3 had its microstructure characterized by Electron Backscatter Diffraction (EBSD) technique and optical microscopy (OM). The corrosion behavior was investigated by exfoliation corrosion (EXCO) test and the intergranular corrosion susceptibility according to ASTM G110-97. After all tests, the samples were observed by scanning electron microscopy (SEM). EBSD results revealed the evolution of microstructure as a result of FSW. The base metal showed elongated grains along the rolling direction with a pancake-like non-recrystallized structure. The SZ undergone dynamic recrystallization showing finer equiaxed grains as a result of a significant plastic deformation and heating during the welding process. The TMAZ of the advancing side showed recrystallized finer grains, while the TMAZ of the retreating side showed coarse grains. Finally, the HAZ of both advancing and retreating sides showed grains typically elongated caused by the thermal input. The EXCO and intergranular tests showed a more intense attack in the TMAZ of the retreating side in agreement with the corrosion morphology observed by SEM.
Effect of galvanic coupling on the corrosion susceptibility of friction stir weldment of AA2198-T851 alloy
2018 - COSTA, I.; DONATUS, U.; MILAGRE, M.X.; MACHADO, C.S.C.; ARAUJO, J.V.S.
The AA2198-T851 alloy is a new generation Al-Li alloy which finds application in the aerospace industry. Its preference over conventional Al alloys is premised on the fact that it exhibits better strength to weight ratio and improved fatigue resistance due to the addition of Li as a major alloying element. However, it is a relatively new alloy and its processing-structure-property-performance relationship is far from being established. This is very true for the relationship between its structure and corrosion resistance which is very scarce in the literature. Our recent findings have revealed that this alloy is highly susceptible to severe localized corrosion which is caused by the abundance of active hexagonal T1 (Al2CuLi) particles in its microstructure. The corrosion susceptibility is further promoted by the non-uniform precipitation of these particles which are often preferentially concentrated in bands aligned parallel to the {111}Al. Furthermore, bulk zonal heterogenities with pronounced non-uniform distribution of the active T1 particles are created when this alloy is welded using friction stir welding. The friction stir welding process is a solid state welding process that has been adjudged to be the best welding technique for Al alloys. Nonetheless, this process generates different zones in the weldments of Al alloys. Thus, zones exhibiting different electrochemical characteristics and severe galvanic interactions can occur when the weldment is exposed to a corrosive media. The galvanic interactions can lead to a faster propagation of attack in the most susceptible region of the weldment, which in this case is the parent material (with the highest volume fraction of the T1 particles). To establish this, the galvanic interactions between the zones of the weldment have been investigated by separately exposing the parent material and the stir zone of the weld and then by exposing the entire weldment using NaCl and EXCO solutions. Optical, scanning electron and transmission electron microscopes were also employed in the study. The results revealed that the parent material of the weldment was the most susceptible (as previously mentioned) and appeared to corrode at a faster rate when coupled to the more cathodic stir zone, thermomechanically affected zone and the heat affected zones of the weldment (with lower volume fraction of the T1 particles). The modes of corrosion in the zones of the weld were also observed to be different. However, the most susceptible region corroded intragranularly with the grain boundaries exhibiting more noble electrochemical characteristics.
Influence of the Alusi® coating on corrosion resistance of press hardened steel
2018 - BOLSANELLO, M.F.; ARAUJO, J.V.S.; COSTA, I.; ROSSI, J.L.
Press hardened steels (PHS) have been used in the last decades by automotive industries to aggregate the improvement of vehicle safety with the reduction of its heavy, also reducing CO2 emissions. This material category, also called ultrahigh strength boron manganese steels, is capable to succeed hot stamping process, a development of the cold stamping process, that avoids spring back and allows the attainment of complex geometries. Hot stamping process consists basically on heating a steel blank until its austenitization, transferring it to press tooling, forming and quenching it to fully martensitic transformation. Besides all the advantages in the final product, the step consisted in the transference from the furnace to the press is critical for the steel, once the absence of a protective atmosphere might promote deleterious steel oxidation. To solve this problem, ArcelorMittal developed a precoated boron steel, with aluminum-silicon metallic coating, named Alusi®. The addition of this metallic layer prevents steel oxidation and peeling, however laboratorial tests indicated that the coating addition affects mechanical properties of the steel substrate, requiring special cares during conformation process. When submitted to elastic deformation, extensive cracks can form in the coating, and affect the corrosion resistance of the steel. To investigate the influence of the Alusi® coating on ultrahigh strength boron manganese steel corrosion resistance, samples of this material were analyzed with and without the coating, and results obtained were compared to evaluate the interference of the coating on the corrosion process. The tests include open circuit potential measurement, to compare the stabilization of the steel with and without the coating; electrochemical impedance spectroscopy, to compare the effectiveness of the corrosion resistance; and immersion trials, interrupted every two hours in order to monitor the formation of corrosion products. The results obtained for the two groups of samples were compared, to weigh the advantages and disadvantages of using the Alusi® on hot stamping process.
The effect of FSW on microstructure and intergranular corrosion of the AA2198- T8 alloy
2018 - MACHADO, C.S.C.; DONATUS, U.; ARAUJO, J.V.S.; KLUMPP, R.E.; MILAGRE, M.X.; GIORJAO, R.A.R.; MOGILI, N.V.V.; COSTA, I.
In this investigation, the intergranular corrosion (IGC) resistance of the AA2198-T8 alloy welded by friction stir welding (FSW) was investigated by ASTM G110-97 test. The different zones resulting from FSW showed distinct resistances to intergranular attack depending on the heating and/or mechanical effects produced by welding. The base metal (BM) was the most susceptible to IGC whereas the thermomechanically affected zone (TMAZ) and the stir zone (SZ), presented the highest resistances to IGC comparatively to the other zones. The results of IGC tests were correlated with those of thermal simulation, microhardness measurements, transmission electron microscopy (TEM) and optical microscopy (OM). The dissimilarities in corrosion resistance of the various zones were associated to differences in hardening phase quantities between the various zones. In the BM and HAZ, T1 phase, the main hardening phase, was found at grain boundaries and it resulted in IGC susceptibility. The slight IGC observed in the SZ and TMAZ was not associated with T1 phase which was rarely found but to another precipitate (T2 phase) which was found preferentially located at the grain boundaries in these zones.
Efeito dos tratamentos termomecânicos T8 e T851 na susceptibilidade a exfoliação e corrosão intergranular da liga AA2198
2018 - ARAUJO, J.V.S.; MACHADO, C.S.C.; MILAGRE, M.X.; COSTA, I.; FERREIRA, R.O.; VIVEIROS, B.G. de
As ligas Al-Cu-Li são ligas avançadas de grande interesse para a indústria aeronáutica devido à baixa densidade e alta resistência mecânica destas. Apesar destas vantages, estas apresentam susceptibilidade a diferentes tipos de corrosão. Além disso, os tratamentos termomecânicos aos quais são submetidas durante o processo de fabricação, afetam a microestrutura destas ligas bem como a resistência à corrosão destas. Existem alguns trabalhos publicados sobre a resistência à corrosão destas ligas, porém nestes trabalhos não se faz um comparação entre os efeitos dos diferentes tratamentos termomecânicos. Neste estudo foi investigado os efeitos dos tratamentos termomecânicos T8 e T851 na susceptibilidade à corrosão por exfoliação e corrosão intergranular (IGC) da liga AA2198, segundo as normas ASTM G34 e ASTM G110, respectivamente. Os resultados mostraram significativas diferenças na microestrutura das duas condições, com liga submetida ao tratamento T8 apresentando grãos alongados enquanto a exposta ao tratamento T851, grãos equaxiais. Ambas as ligas apresentaram suscetibilidade a exfoliação. Entreanto, enquanto a liga T8 apresentou susceptibilidade à corrosão intergranular e intragranular, a liga T851 não foi suscetível à corrosão intergranular, apresentando ataque de corrosão dentro dos grãos, ou seja, corrosão intragranular.
Comparação da resistência a corrosão localizada de ligas de alumínio pela técnica de varredura com eletrodo vibratório (SVET)
2018 - MILAGRE, M.X.; ARAUJO, J.S.; MACHADO, C.S.C.; DONATUS, U.; COSTA, I.
As ligas Alumínio-Cobre-Lítio (Al-Cu-Li) foram desenvolvidas como substitutas para as ligas convencionais de Al-Cu. Apesar de apresentarem melhor módulo específico também são suscetíveis à corrosão localizada. As técnicas eletroquímicas convencionais são ferramentas úteis para entender o comportamento de corrosão das ligas de Al, no entanto elas dão uma resposta global dos fenômenos de corrosão. Neste trabalho, a técnica de varredura com eletrodo vibratório (SVET) foi utilizada para comparar os mecanismos de corrosão de algumas ligas de Al. Os ensaios com SVET foram realizados em solução de NaCl 0,005 mol L-1 durante 24 h e os mapas foram obtidos a cada 2 h para as ligas AA2024-T3, AA2098-T351 e AA2198-T851. Os resultados mostraram diferentes mecanismos para cada liga sendo que as ligas Al- Cu-Li maiores densidades de corrente associadas a corrosão severa localizada em relação a liga AA2024-T3.
EIS study of the microstructure influence on the corrosion behaviour of AA 2198-T3 compared to AA 2198-T851 alloy
2016 - ARAUJO, J.V. de S.; QUEIROZ, F.M.; TERADA, M.; ASTARITA, A.; COSTA, I.
This paper deals with the study of the influence of the temper state on the electrochemical behavior of an high strength aluminum-lithium alloy. In particular the corrosion resistance of the AA2198 alloy in both T3 and T851 temper condition, has been evaluated by immersion tests as a function of immersion time in NaCl 0.01 mol.L-1. The evolution of the electrochemical behavior was monitored by electrochemical impedance spectroscopy (EIS) and surface observation by optical microscopy and Field Emission Gun- Scanning Electron Microscopy. The results indicated a higher electrochemical activity associated to the T851 treatment comparatively to the T3 one and this was ascribed to the more heterogeneous microstructure related to the first treatment. Severe localized corrosion was seen on the AA2198-T851 alloy after only few hours of exposure to the test medium. This type of corrosion was of the crystallographic type and was related to T1 (Al2LiCu) which is more electrochemically active than the matrix leading to localized attack. Pitting attack was seen on the AA2198-T3 alloy along the surface and it was located at the matrix-precipitates interface. The EIS results supported a faster kinetics and lower impedances associated to the AA2198-T851 comparatively to the AA2198-T3 alloy according to the surface observation along the test period.